The overall objective of this project is to develop a novel visual homogenous immunoassay (VIA) for the rapid diagnosis of sexually transmitted infections. The design of this remarkably simple assay will be demonstrated for the serologic diagnosis of syphilis. A recombinant fusion protein comprising a single chain Fv (scFv) fragment of an anti- human glycophorin A monoclonal antibody and the T. pallidum TmpA protein will be genetically linked, expressed and purified. When mixed with a drop of blood, this fusion protein will sensitize the subject's erythrocytes enabling antibodies against T. pallidum to be identified by agglutination. This fusion protein is seen as the basis for a fast and simple visual immunoassay (VIA) for the serologic diagnosis of syphilis. In phase l, we accomplished all of our aims. Specifically, we prepared and expressed a scFv form of an antiglycophorin monoclonal antibody (MAB), linked this scFv to T. pallidum antigen TmpA and demonstrated that this scFv-TmpA fusion protein was active as a novel VIA. The goals of phase II are to 1) evaluate and optimize performance of the homogenous assay; 2) scale-up production and 3) establish assay variability, quality control, etc. Finally, we will evaluate performance on clinical samples in collaboration with the Division of AIDS, STDs and Tuberculosis Laboratory Research at the CDC. PROPOSED COMMERCIAL APPLICATIONS: Development of a series of homogenous assays based on the technology to be developed herein will have significant commercial potential for syphilis as well as other infectious diseases.